Polyaxial pedicle screw having a rotating locking element

ABSTRACT

A screw and coupling element assembly for use with an orthopedic rod implantation apparatus includes a screw with a head and a shaft extending from the head, a coupling element with a seat within which the head is seatable such that the shaft protrudes from the coupling element, and a locking element mateable with the coupling element and when mated is selectively movable through a plurality of positions including unlocked and locked positions. When in the unlocked position, the locking element presents a rod-receiving channel and the head is movable in the seat such that the shaft is directable in a plurality of angles relative to the coupling element. When in the locked position, a rod disposed within the rod-receiving channel is fixed relative to the coupling element and the head is immovable in the seat such that the shaft is fixed at an angle relative to the coupling element.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuing application of U.S. patent applicationSer. No. 10/115,747 entitled “Polyaxial Pedicle Screw Having a RotatingLocking Element”, filed Apr. 3, 2002, which is a continuationapplication of U.S. patent application Ser. No. 09/789,935, filed Feb.15, 2001, now U.S. Pat. No 6,451,021, the disclosures of which arehereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The invention relates generally to screws and coupling elementassemblies for use with orthopedic fixation systems. More particularly,the invention relates to a screw and coupling element assembly, for usewith an orthopedic rod implantation apparatus, that includes a lockingelement that simultaneously locks a head of the screw within a seat ofthe coupling element so that a shaft of the screw is fixed at an anglerelative to the coupling element and a rod, of the orthopedic rodimplantation apparatus, disposed within a rod-receiving channel of thelocking element is fixed relative to the coupling element.

BACKGROUND OF THE INVENTION

The bones and connective tissue of an adult human spinal column consistsof more than twenty discrete bones coupled sequentially to one anotherby a tri-joint complex which consist of an anterior disc and the twoposterior facet joints, the anterior discs of adjacent bones beingcushioned by cartilage spacers referred to as intervertebral discs.These more than twenty bones are anatomically categorized as beingmembers of one of four classifications: cervical, thoracic, lumbar, orsacral. The cervical portion of the spine, which comprises the top ofthe spine, up to the base of the skull, includes the first sevenvertebrae. The intermediate twelve bones are the thoracic vertebrae, andconnect to the lower spine comprising the five lumbar vertebrae. Thebase of the spine is the sacral bones (including the coccyx). Thecomponent bones of the cervical spine are generally smaller than thoseof the thoracic and lumbar spine.

Referring now to FIGS. 1, 2, and 3, top, side, and posterior views of avertebral body, a pair of adjacent vertebral bodies, and a sequence ofvertebral bodies are shown, respectively. The spinal cord is housed inthe central canal 10, protected from the posterior side by a shell ofbone called the lamina 12. The lamina 12 includes a rearwardly anddownwardly extending portion called the spinous process 16, andlaterally extending structures which are referred to as the transverseprocesses 14. The anterior portion of the spine comprises a set ofgenerally cylindrically shaped bones which are stacked one on top of theother. These portions of the vertebrae are referred to as the vertebralbodies 20, and are each separated from the other by the intervertebraldiscs 22. The pedicles 24 comprise bone bridges which couple theanterior vertebral body 20 to the corresponding lamina 12.

The spinal column of bones is highly complex in that it includes overtwenty bones coupled to one another, housing and protecting criticalelements of the nervous system having innumerable peripheral nerves andcirculatory bodies in close proximity. In spite of these complexities,the spine is a highly flexible structure, capable of a high degree ofcurvature and twist in nearly every direction. Genetic or developmentalirregularities, trauma, chronic stress, tumors, and disease, however,can result in spinal pathologies which either limit this range ofmotion, or which threaten the critical elements of the nervous systemhoused within the spinal column. A variety of systems have beendisclosed in the art which achieve this immobilization by implantingartificial assemblies in or on the spinal column. These assemblies maybe classified as anterior, posterior, or lateral implants. As theclassifications suggest, lateral and anterior assemblies are coupled tothe anterior portion of the spine, which is the sequence of vertebralbodies. Posterior implants generally comprise pairs of rods, which arealigned along the axis which the bones are to be disposed, and which arethen attached to the spinal column by either hooks which couple to thelamina or attach to the transverse processes, or by screws which areinserted through the pedicles.

“Rod assemblies” generally comprise a plurality of such screws which areimplanted through the posterior lateral surfaces of the laminae, throughthe pedicles, and into their respective vertebral bodies. The screws areprovided with upper portions which comprise coupling elements, forreceiving and securing an elongate rod therethrough. The rod extendsalong the axis of the spine, coupling to the plurality of screws viatheir coupling elements. The rigidity of the rod may be utilized toalign the spine in conformance with a more desired shape.

It has been identified, however, that a considerable difficulty isassociated with inserting screws along a misaligned curvature andsimultaneously exactly positioning the coupling elements such that therod receiving portions thereof are aligned so that the rod can be passedtherethrough without distorting the screws. Attempts at achieving properalignment with fixed screws is understood to require increased operatingtime, which is known to enhance many complications associated withsurgery. Often surgical efforts with such fixed axes devices cannot beachieved, thereby rendering such instrumentation attempts entirelyunsuccessful.

The art contains a variety of attempts at providing instrumentationwhich permit a limited freedom with respect to angulation of the screwand the coupling element. These teachings, however, are generallycomplex, inadequately reliable, and lack long-term durability. Theseconsiderable drawbacks associated with prior art systems also includedifficulty in properly positioning the rod and coupling elements, andthe tedious manipulation of the many parts that are used in the priorart to lock the rod, the screw, and the coupling element in positiononce they are properly positioned. It is not unusual for displacement tooccur as these parts are manipulated to lock the elements, which isclinically unacceptable, and repeated attempts at locking the elementsin proper position must be made to remedy this displacement.

There is, therefore, a need for a screw and coupling element assemblywhich provides a polyaxial freedom of implantation angulation withrespect to rod reception. There is also a need for such an assemblywhich comprises a reduced number of elements, and which correspondinglyprovides for expeditious implantation. There is also a need for such anassembly that provides reduced difficulty in locking steps to preventunwanted displacement of the elements prior to locking. There is also aneed for an assembly which is reliable, durable, and provides long termfixation support.

SUMMARY OF THE INVENTION

The invention provides a screw and coupling element assembly for usewith an orthopedic rod implantation apparatus. The assembly includes asecuring element such as, for example, a screw, that has a head and ashaft that extends from the head. Preferably, the head has an engagementsurface that can be engaged by a screwdriving tool. Preferably, the headalso has a curvate proximal portion from which the shaft extends.

The screw and coupling element assembly further includes a couplingelement and a locking element. The coupling element has a seat withinwhich the head of the screw can be seated such that the shaft of thescrew protrudes from the coupling element. The locking element can bemated with the coupling element and thereafter can be selectively movedthrough a plurality of positions including an unlocked position and alocked position. When the locking element is in the unlocked position,the locking element presents a rod-receiving channel and the head of thescrew is movable in the seat of the coupling element, such that theshaft of the screw can be directed in a plurality of angles relative tothe coupling element. When the locking element is in the lockedposition, a rod disposed within the rod-receiving channel is fixedrelative to the coupling element, and the head of the screw is immovablein the seat of the coupling element, such that the shaft of the screw isfixed at an angle relative to the coupling element. More particularly,when the locking element is in the locked position, the locking elementis compression locked within the coupling element, the head of the screwis compression locked within the seat of the coupling element, and therod is compression locked within the rod-receiving channel.

Preferably, at least one feature on the locking element can be used tomove the locking element through the positions when the locking elementis disposed within the coupling element. Preferably, the featurecomprises an engagement surface that can be engaged by a correspondingsurface of a tool, such that the tool can engage the engagement surfaceof the feature and effectively move the locking element. Preferably, thecorresponding surface of the tool can engage the engagement surface ofthe feature despite the presence of the rod in the rod-receivingchannel.

Preferably, the seat of the coupling element can be defined by a bore inthe coupling element and a socket defined by a curvate volume adjacentthe bore. The curvate volume corresponds to the curvate proximal portionof the head of the screw such that the curvate proximal portion can benested in the socket. When the curvate proximal portion of the head ofthe screw is nested in the socket, the shaft of the screw protrudes fromthe bore and the curvate proximal portion cannot pass fully through thebore. When the locking element is in the unlocked position, the curvateproximal portion of the head of the screw can rotate and angulate in thesocket such that the shaft of the screw can be directed through a rangeof angles relative to the coupling element. When the locking element isin the locked position, the curvate proximal portion of the head of thescrew is immovable in the socket such that the shaft of the screw isfixed at an angle relative to the coupling element.

Preferably, the locking and unlocking action of the locking element iseffected as follows. The head of the screw has a distal portion definedby a compression surface and the locking element has a permissivesurface that is presented to the compression surface of the head of thescrew when the locking element is in the unlocked position. Whenpresented with the permissive surface of the locking element, thecompression surface of the head of the screw is unhindered such that thehead of the screw is movable in the seat of the coupling element. Thelocking element also has a confrontational surface that is presented tothe compression surface of the head of the screw when the lockingelement is in the locked position. The confrontational surface of thelocking element is defined by a recess that has a recessed surfacecorresponding to the compression surface of the head of the screw.Therefore, when the locking element is in the locked position: (1) thelocking element is compressed within the coupling element, (2) thecompression surface of the head of the screw is compressed by theconfrontational surface of the locking element such that the curvateproximal portion of the head of the screw is compressed toward the boreof the coupling element and the head of the screw is immovable in theseat of the coupling element, and (3) the compression surface of thehead of the screw seats in the recess of the confrontational surface andthereby is biased against retreat from the recess. The compressionsurface of the head of the screw can be a curvate surface and theconfrontational surface of the locking element can extend from an edgeof the permissive surface of the locking element and terminate in therecess of the confrontational surface. The confrontational surface ofthe locking element preferably becomes increasing confrontational andtherefore is gradually presented to the compression surface of the headof the screw as the locking element is moved from the unlocked positionto the locked position.

Preferably, the rod-receiving channel, presented by the locking elementwhen the locking element is in the unlocked position, is defined bysubstantially parallel walls. When the locking element is in the lockedposition, the walls are compressed toward one another such that the rodis compressed within the channel and thereby fixed relative to thecoupling element. Preferably, the walls are increasingly compressedtoward one another as the locking element is moved from the unlockedposition to the locked position.

Preferably, the coupling element has a bore that permits use of thescrewdriving tool when the head is seated in the seat, allowing thescrewdriving tool to engage the head as described above. Alsopreferably, the locking element has a bore that permits use of thescrewdriving tool when the locking element is disposed within thecoupling element in an unlocked position and the head is seated in theseat, allowing the screwdriving tool to engage the head as describedabove.

A use of the invention can be summarized as follows. First, the lockingelement is disposed within the coupling element. Then, the lockingelement is rotated within the coupling element until the locking elementis in the unlocked position. The top bores of the locking element andthe coupling element will then permit the insertion of the screw intothe seat of the coupling element. The surgeon can freely rotate andangulate the screw in the socket to direct the shaft in the clinicallyappropriate direction for secure lodging in a vertebral bone.

Once the surgeon directs the shaft of the screw in the clinicallyappropriate direction, he passes the operative end of the screwdrivingtool through the top bores to engage the head of the screw to rotate thescrew and drive the shaft of the screw into the vertebral bone. Apre-drill hole is usually provided in the bone, into which it is desiredthat the screw be disposed.

Typically, the surgeon will repeat the process described above usingadditional screws, coupling elements, and locking elements, lodging theadditional screws into the same vertebral bone or other vertebral bones,depending on the clinically desirable result. To that end, the inventionencompasses an orthopedic rod implantation apparatus having a pluralityof screws and coupling elements of the types described above, and atleast one elongate rod. Many implantations will require the use of tworods, however, only one rod or more than two rods may be necessary. Thesurgeon will, for example, lodge two screws into a first verterbal bone(the screws are positioned laterally adjacent one another in the samebone, one in each pedicle), and lodge two other screws into a secondvertebral bone (the screws are positioned laterally adjacent one anotherin the same bone, one in each pedicle) that may be adjacent the firstvertebral bone or may be separated from the first vertebral bone byother vertebral bones that are damaged or unstable.

In a healthy spine, each screw in one of the pairs would roughly alignwith the corresponding screw in the other pair, because the vertebralbones would be vertically aligned. However, in some cases, the screwswill not be aligned because the spine is laterally crooked and thesurgeon is installing the implant to realign the vertebral bones.Therefore, in such cases, once the screws are in place, and theassociated coupling elements and locking elements are in the unlockedposition, presenting respective rod-receiving channels, and free torotate and angulate with respect to the head of the associated screw,the surgeon inserts a rod into one rod-receiving channel, and thereafterinto another rod-receiving channel, so that the rod lines up theverterbral bones affected thereby in a clinically desirable manner,urging them, typically, into vertical alignment. The surgeon similarlyinserts a second rod into the remaining two rod receiving channels tobalance the alignment forces.

Once the rods are in the rod receiving channels, the surgeon proceeds tomove each locking element into the locked position by rotating thelocking element. As the locking element is moved to the locked position,the permissive surface, of the locking element, that is presented to thecompression surface of the head of the screw when the locking element isin the unlocked position, is removed and the compression surface isincreasingly presented with the confrontational surface. This causes thecurvate proximal portion of the head of the screw to be increasinglycompressed toward the bore until the head is immovable in the seat ofthe coupling element. Ultimately, the compression surface seats in therecess and thereby is biased against retreat from the recess. Thisprevents accidental reverse rotational slippage of the locking elementfrom occurring and moving the locking element to the unlocked position.

In addition, as the locking element is moved to the locked position, therod-receiving channel presented by the locking element when the lockingelement is in the unlocked position gradually closes. Ultimately, thechannel is completely closed. This prevents the rod from laterallyexiting the locking element. Further, the walls of the channel aregradually compressed toward one another, until they ultimately securethe rod between them so that the rod is fixed relative to the couplingelement. This prevents the rod from axially exiting the locking element.

In addition, as the locking element is moved to the locked position, thelocking element itself is gradually compressed within the couplingelement until it ultimately is secured within the coupling element. Morespecifically, as the rod seeks to radially force the walls and apart,the outer surface of the locking element seeks to radially push againstthe inner surface of the coupling element. However, the structuralintegrity of the coupling element resists the radial force of thelocking element, and the locking element is secured in the couplingelement thereby. This prevents the locking element from axially exitingthe coupling element.

In this manner, once the locking element is moved to the lockedposition, the screw, the coupling element, the locking element, and therod are all fixed relative to one another and to the bone. When all ofthe locking elements are so positioned, the implant is installed. Afterthe surgeon moves all of the locking elements in the orthopedic rodimplantation apparatus to the locked position, he closes the wounds ofthe patient and the surgery is complete.

Multiple screw and coupling element assemblies are generally necessaryto complete the full array of anchoring sites for a rod immobilizationsystem, however, the screw and coupling element assembly of theinvention is designed to be compatible with alternative rod systems sothat, where necessary, the invention may be employed to rectify thefailures of other systems, the implantation of which may have alreadybegun.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a human vertebra.

FIG. 2 is a side view of a pair of adjacent vertebrae of the type shownin FIG. 1.

FIG. 3 is a posterior view of a sequence of vertebrae of the type shownin FIGS. 1 and 2.

FIGS. 4a, 4 b and 4 c are side, top, and cutaway side views of a screwsuitable for use in the invention.

FIGS. 4d and 4 e are side cutaway views of a screwdriving tool suitablefor driving the screw of FIGS. 4a, 4 b and 4 c.

FIGS. 5a, 5 b and 5 c are front, side and top views of a couplingelement suitable for use in the invention.

FIGS. 6a, 6 b, 6 c, 6 d and 6 e are front, side, front cutaway, sidecutaway, and top views of a locking element suitable for use in theinvention.

FIG. 7 is a front cutaway view of the screw of FIGS. 4a-c, the couplingelement of FIGS. 5a-c, the locking element of FIGS. 6a-e, and a rod,with the locking element in an unlocked position.

FIG. 8 is front view of the screw of FIGS. 4a-c, the coupling element ofFIGS. 5a-c, the locking element of FIGS. 6a-e, and a rod, with thelocking element in a locked position.

FIG. 9 is a side cutaway view of the screw of FIGS. 4a-c, the couplingelement of FIGS. 5a-c, the locking element of FIGS. 6a-e, and thescrewdriving tool of FIGS. 4d-e.

FIGS. 10a and 10 b are front and side cutaway views of a wrenching toolsuitable for wrenching hexagonal protrusions of the locking element ofFIGS. 6a-e.

DETAILED DESCRIPTION OF THE INVENTION

While the invention will be described more fully hereinafter withreference to the accompanying drawings, in which particular embodimentsand methods of implantation are shown, it is to be understood at theoutset that persons skilled in the art may modify the invention hereindescribed while achieving the functions and results of this invention.Accordingly, the descriptions which follow are to be understood asillustrative and exemplary of specific structures, aspects and featureswithin the broad scope of the invention and not as limiting of suchbroad scope.

In an embodiment, the invention provides a screw and coupling elementassembly for use with an orthopedic rod implantation apparatus. Theassembly includes a securing element such as, for example, a screw, thathas a head and a shaft that extends from the head. Other securingelements can include, for example, lamina hooks and sacral blocks.

Accordingly, FIG. 4a illustrates a side view of a screw 120 suitable foruse in the invention. The screw 120 includes a head 122 and a shaft 126that extends from the head 122. The shaft 126 is shown as having atapered shape with a high pitch thread 128. It shall be understood thata variety of shaft designs are interchangeable with the screw of theinvention. The specific choice of shaft features, such as thread pitch,shaft diameter to thread diameter ratio, and overall shaft shape, shouldbe made be the physician with respect to the conditions of theindividual patient's bone, however, the invention is compatible with awide variety of shaft designs.

Preferably, the head has an engagement surface that can be engaged by ascrewdriving tool. In this regard, one of the head and the tool can havea polygonal recess and the other of the head and the tool can have anexternal structure that fits within the recess.

Accordingly, referring again to FIG. 4a and also to FIGS. 4b-4 e, thehead 122 of the illustrated screw 120 includes a hexagonal engagementsurface 130 that fits within a hexagonal recess 140 a of a screwdrivingtool 140. The surface 130 defines a receiving locus for the applicationof a torque for driving the screw 120 into a vertebral bone. Of course,the specific shape of the surface 130 may be chosen to cooperate withany suitable screwdriving tool. For example, the surface 130 may includean engagement surface of another shape, or a recess such as, forexample, a slot for receiving a standard screwdriver, a hexagonallyshaped hole for receiving an allen wrench, or a threading for acorrespondingly threaded post. Preferably, the surface 130 is co-axialwith the generally elongate axis of the screw 120 and, mostparticularly, the shaft 126. Having the axes of the surface 130 and theshaft 126 co-linear facilitates step of inserting the screw 120 into thebone.

Preferably, the head has a curvate proximal portion from which the shaftextends. The curvate proximal portion can be a semi-spherical shape,exhibiting an external contour that is equidistant from a center pointof the head. When the head has an engagement surface that can be engagedby a screwdriving tool, it is preferable that the engagement surfacedoes not disrupt the functionality of the curvate proximal portion asdescribed herein.

Accordingly, referring also to FIG. 4a again, the head 122 of theillustrated screw 120 includes a hemisphere 122 a as the curvateproximal portion. The use of the hemisphere 122 a in this embodimentfrees the hexagonal engagement surface 130 to effectively receive thehexagonal recess 140 a of the screwdriving tool 140.

Further, the head 122 of the illustrated screw 120 is connected to theshaft 126 at a neck 124. The diameter of the head 122 is equal to thelargest diameter of the shaft 126, and the neck 124 tapers to expose theoperative portions of the curvate proximal portion 122 a of the head122. This configuration permits the screw 120 to swing through a varietyof angles before its position is fixed, as described below. It should benoted that in other embodiments, the diameter of the shaft 126 can beless than or greater than the diameter of the head 122, and the neck 124may be un-tapered or differently tapered.

In this embodiment, the screw and coupling element assembly furtherincludes a coupling element and a locking element. The coupling elementhas a seat within which the head of the screw can be seated such thatthe shaft of the screw protrudes from the coupling element. The lockingelement can be mated with the coupling element and thereafter can beselectively moved through a plurality of positions including an unlockedposition and a locked position. When the locking element is in theunlocked position, the locking element presents a rod-receiving channeland the head of the screw is movable in the seat of the couplingelement, such that the shaft of the screw can be directed in a pluralityof angles relative to the coupling element. When the locking element isin the locked position, a rod disposed within the rod-receiving channelis fixed relative to the coupling element, and the head of the screw isimmovable in the seat of the coupling element, such that the shaft ofthe screw is fixed at an angle relative to the coupling element. Moreparticularly, when the locking element is in the locked position, thelocking element is compression locked within the coupling element, thehead of the screw is compression locked within the seat of the couplingelement, and the rod is compression locked within the rod-receivingchannel. At least one feature on the locking element can be used to movethe locking element through the positions when the locking element isdisposed within the coupling element. Preferably, the feature comprisesan engagement surface that can be engaged by a corresponding surface ofa tool, such that the tool can engage the engagement surface of thefeature and effectively move the locking element. Preferably, thecorresponding surface of the tool can engage the engagement surface ofthe feature despite the presence of the rod in the rod-receivingchannel.

Accordingly, FIGS. 5a-c illustrate a coupling element 150 suitable foruse in the invention, in front, top, side, front cutaway, and sidecutaway views, respectively. FIGS. 6a-e illustrate a locking element 185suitable for use in the invention, in front, top, and side views,respectively. FIG. 7 illustrates a front cutaway view of the screw 120of FIG. 4, the coupling element 150, and the locking element 185disposed within the coupling element 150 in an unlocked position. FIG. 8illustrates a front view of the screw 120 of FIG. 4, the couplingelement 150, and the locking element 185 disposed within the couplingelement 150 in a locked position. The coupling element 150 has asubstantially cylindrical inner surface 150 c that accepts a cylindricalouter surface 185 e of the locking element 185 for coaxial insertion androtational translation therein so the locking element 185 can be rotatedthrough a plurality of positions. At one extreme of the positionalspectrum enjoyed by this locking element 185 is the unlocked positionshown in FIG. 7. At the other extreme is the locked position shown inFIG. 8. In order to permit the locking element 185 to be moved throughthe positions, the locking element 185 has a feature on each end of thelocking element 185, having a surface defined by a hexagonal protrusion185 d extending beyond a respective end of the coupling element 150. Thehexagonal protrusions 185 d can each be engaged by a correspondingsurface of a tool such as, for example, the corresponding hexagonalrecess 142 a of the wrenching tool 142 shown in FIGS. 10a and 10 b. Sothat the hexagonal recess 142 a can engage the hexagonal protrusions 185d despite the presence of a rod 195 in a rod-receiving channel 190, thewrenching tool 142 has a slot 142 b that accommodates the rod 195 as thewrenching tool 142 is rotated to rotate the locking element 185.

Preferably, the seat of the coupling element can be defined by a bore inthe coupling element and a socket defined by a curvate volume adjacentthe bore. The curvate volume corresponds to the curvate proximal portionof the head of the screw such that the curvate proximal portion can benested in the socket. When the curvate proximal portion of the head ofthe screw is nested in the socket, the shaft of the screw protrudes fromthe bore, the curvate proximal portion cannot pass fully through thebore. When the locking element is in the unlocked position, the curvateproximal portion of the head of the screw can rotate and angulate in thesocket such that the shaft of the screw can be directed through a rangeof angles relative to the coupling element. When the locking element isin the locked position, the curvate proximal portion of the head of thescrew is immovable in the socket such that the shaft of the screw isfixed at an angle relative to the coupling element.

Accordingly, referring to FIGS. 5a-c, 6 a-e and 7-8, a seat 150 a of theillustrated coupling element 150 is defined by a bore 150 b in thecoupling element 150 and a socket defined by a curvate volume 150 cadjacent the bore 150 b. The curvate volume 150 c corresponds to thecurvate proximal portion 122 a of the head 122 such that the curvateproximal portion 122 a can be nested in the socket 150 c. It isunderstood that the head 122 of the screw 120 is held within the curvatevolume 150 c by the relative size of the curvate proximal portion 122 aas compared with the bore 150 b. More specifically, the bore 150 b has adiameter less than the diameter of the curvate proximal portion 122 a.When the curvate proximal portion 122 a is nested in the socket 150 c,the shaft 126 protrudes from the bore 150 a and the curvate proximalportion 122 a cannot pass fully through the bore 150 a. Further when thecurvate proximal portion 122 a is nested in the socket 150 c, and whenthe locking element 185 is in the unlocked position, the curvateproximal portion 122 a can rotate and angulate in the socket 150 c suchthat the shaft 126 can be directed through a range of angles relative tothe coupling element 150. Further when the curvate proximal portion 122a is nested in the socket 150 c, and when the locking element 185 is inthe locked position, the curvate proximal portion 122 a is immovable inthe socket 150 c such that the shaft 126 is fixed at an angle relativeto the coupling element 150.

Preferably, the locking and unlocking action of the locking element iseffected as follows. The head of the screw has a distal portion definedby a compression surface and the locking element has a permissivesurface that is presented to the compression surface of the head of thescrew when the locking element is in the unlocked position. Whenpresented with the permissive surface of the locking element, thecompression surface of the head of the screw is unhindered such that thehead of the screw is movable in the seat of the coupling element. Thelocking element also has a confrontational surface that is presented tothe compression surface of the head of the screw when the lockingelement is in the locked position. The confrontational surface of thelocking element is defined by a recess that has a recessed surfacecorresponding to the compression surface of the head of the screw.Therefore, when the locking element is in the locked position: (1) thelocking element is compressed within the coupling element, (2) thecompression surface of the head of the screw is compressed by theconfrontational surface of the locking element such that the curvateproximal portion of the head of the screw is compressed toward the boreof the coupling element and the head of the screw is immovable in theseat of the coupling element, and (3) the compression surface of thehead of the screw seats in the recess of the confrontational surface andthereby is biased against retreat from the recess. The compressionsurface of the head of the screw can be a curvate surface and theconfrontational surface of the locking element can extend from an edgeof the permissive surface of the locking element and terminate in therecess of the confrontational surface. The confrontational surface ofthe locking element preferably becomes increasing confrontational andtherefore is gradually presented to the compression surface of the headof the screw as the locking element is moved from the unlocked positionto the locked position.

Accordingly, referring to FIGS. 5a-c, 6 a-e and 7-8, the illustratedhead 122 has a distal portion defined by a compression surface 122 b andthe illustrated locking element 185 has a permissive surface 185 a thatis presented to the compression surface 122 b when the locking element185 is in the unlocked position. When presented with the permissivesurface 185 a, the compression surface 122 b is unhindered such that thehead 122 is movable in the seat 150 a. Further, the illustrated lockingelement 185 has a confrontational surface 185 b that is presented to thecompression surface 122 b when the locking element 185 is in the lockedposition. The confrontational surface 185 b is defined by a recess 185 cthat has a recessed surface corresponding to the compression surface 122b. When the illustrated locking element 185 is in the locked position,(1) the locking element 185 is compressed within the coupling element150, (2) the compression surface 122 a is compressed by theconfrontational surface 185 b such that the curvate proximal portion 122a of the head 122 is compressed toward the bore 150 b and the head 122is immovable in the seat 150 a, and (3) the compression surface 122 bseats in the recess 185 c and thereby is biased against retreat from therecess 185 c. The illustrated compression surface 122 a is a curvatesurface and the confrontational surface 185 b extends from an edge ofthe permissive surface 185 a and terminates in the recess 185 c. Theconfrontational surface 185 b is tapered to become increasingconfrontational as the locking element 185 is moved from the unlockedposition to the locked position and therefore is gradually presented tothe compression surface 122 a as the locking element 185 is moved fromthe unlocked position to the locked position.

Preferably, the rod-receiving channel, presented by the locking elementwhen the locking element is in the unlocked position, is defined bysubstantially parallel walls. When the locking element is in the lockedposition, the walls are compressed toward one another such that the rodis compressed within the channel and thereby fixed relative to thecoupling element. Preferably, the walls are increasingly compressedtoward one another as the locking element is moved from the unlockedposition to the locked position.

Accordingly, referring to FIGS. 5a-c, 6 a-e and 7-8, the rod-receivingchannel 190 that is presented by locking element 185 when the lockingelement 185 is in the unlocked position has substantially parallel walls190 a, 190 b. As the locking element 185 is moved from the unlockedposition to the locked position, the walls 190 a, 190 b are increasinglycompressed toward one another. When the locking element 185 is in thelocked position, the walls 190 a, 190 b are compressed toward oneanother such that the rod 195 is compressed within the channel 190 andthereby fixed relative to the coupling element 150.

Preferably, the coupling element has a bore that permits use of thescrewdriving tool when the head is seated in the seat, allowing thescrewdriving tool to engage the head as described above. Alsopreferably, the locking element has a bore that permits use of thescrewdriving tool when the locking element is disposed within thecoupling element in an unlocked position and the head is seated in theseat, allowing the screwdriving tool to engage the head as describedabove.

Accordingly, with reference also to FIGS. 5a-c, 6 a-e, 7 and 8, FIG. 9illustrates a side cutaway view of the screw 120, coupling element 150,locking element 185, and screwdriving tool 140. It can be seen that atop surface of the coupling element 150 has a bore 197 through which thescrewdriving tool 140, which is used to insert the screw 120 into thebone, may access and rotate the screw 120 through the coupling element150. It can also be seen that a top surface of the locking element 150has a bore 199 through which the screwdriving tool 140 may access androtate the screw 120 through the locking element 185 when the lockingelement 185 is in the unlocked position.

Referring now to FIGS. 5a-c, 6 a-e, 7-9 and 10 a-10 b, the preferredmethod of implantation and assembly is described hereinbelow. First, thelocking element 185 is disposed within the coupling element 150 so thatit can be selectively moved. This can be accomplished by coaxiallyinserting the locking element 185 into the coupling element 150,contacting the cylindrical outer surface of the locking element 185 withthe substantially cylindrical inner surface 150 c of the couplingelement 150.

Once the locking element 185 is disposed within the coupling element 150in this manner, the wrenching tool 142 shown in FIGS. 10a-10 b can beused to engage the hexagonal protrusions 185 d of the locking element185 and rotate the locking element 195 within the coupling element 150until the locking element 185 is in the unlocked position as shown inFIG. 7.

When the locking element 185 is in the unlocked position, the bore 199of the locking element and the bore 197 of the coupling element permitthe insertion of the screw 120 into the seat 150 a. More particularly,the surgeon can pass the shaft 126 of the screw 120 and the head 122 ofthe screw through the bores 199 and 197, but only the shaft 126 willpass through the bore 150 b of the coupling element 150. As statedabove, the curvate proximal portion 122 a of the head 122 will not passthrough the bore 150 b, but instead will nest in the seat 150 a in thecurvate volume 150 c of the coupling element 150. The surgeon is thenable to freely rotate and angulate the screw 120 in the socket 150 c todirect the shaft 126 in the clinically appropriate direction for securelodging in a vertebral bone.

It should be noted that while the insertion of the locking element 185into the coupling element 150 and the subsequent insertion of the screw120 through the bores 199 and 197 has been described, it is possible topre-assemble these elements in this configuration prior to delivery tothe surgeon to minimize the effort and time required from the surgeon inpreparing the elements for operative use.

Once the surgeon directs the shaft 126 of the screw 120 in theclinically appropriate direction, he is able to pass the operative endof the screwdriving tool 140 shown in FIGS. 4d and 4 e through the bore199 and the bore 197 to engage the hexagonal engagement surface 130 ofthe head 122 of the screw 120. As stated above, the operative end of thescrewdriving tool 140 has a hexagonal recess 140 a for engaging thehexagonal engagement surface 130 and rotating the screw 120 to drive theshaft 126 of the screw 120 into the vertebral bone. A pre-drill hole isusually provided in the bone, into which it is desired that the screw120 be disposed. The hole may be pre-tapped, or the external threading128 of the screw 120 may include a self-tapping edge.

Typically, the surgeon will repeat the process described above usingadditional screws, coupling elements, and locking elements, lodging theadditional screws into the same vertebral bone or other vertebral bones,depending on the clinically desirable result. To that end, the inventionencompasses an orthopedic rod implantation apparatus having a pluralityof screws and coupling elements of the types described above, and atleast one elongate rod. Many implantations will require the use of tworods, however, only one rod or more than two rods may be necessary. Thesurgeon will, for example, lodge two screws into a first verterbal bone(the screws are positioned laterally adjacent one another in the samebone, one in each pedicle), and lodge two other screws into a secondvertebral bone (the screws are positioned laterally adjacent one anotherin the same bone, one in each pedicle) that may be adjacent the firstvertebral bone or may be separated from the first vertebral bone byother vertebral bones that are damaged or unstable.

In a healthy spine, each screw in one of the pairs would roughly alignwith the corresponding screw in the other pair, because the vertebralbones would be vertically aligned. However, in some cases, the screwswill not be aligned because the spine is laterally crooked and thesurgeon is installing the implant to realign the vertebral bones.Therefore, in such cases, once the screws are in place, and theassociated coupling elements and locking elements are in the unlockedposition, presenting respective rod-receiving channels, and free torotate and angulate with respect to the head of their associated screw,the surgeon inserts a rod into one rod-receiving channel, and thereafterinto another rod-receiving channel, so that the rod lines up theverterbral bones affected thereby in a clinically desirable manner,urging them, typically, into vertical alignment. The surgeon similarlyinserts a second rod into the remaining two rod receiving channels tobalance the alignment forces.

Once the rods are in the rod receiving channels, the surgeon proceeds tomove each locking element 185 into the locked position shown in FIG. 8.The surgeon uses the wrenching tool 142 shown in FIGS. 10a and 10 b,engaging the hexagonal recess 142 a of the wrenching tool 142 with oneof the hexagonal protrusions 185 d of the locking element and moving thewrenching tool 142 to rotate the hexagonal protrusion 185 d and therebyrotate the locking element 185. As the locking element 185 is moved tothe locked position, the permissive surface 185 a, of the lockingelement 185, that is presented to the compression surface 122 b of thehead 122 when the locking element 185 is in the unlocked position, isremoved and the compression surface 122 b is increasingly presented withthe confrontational surface 185 b. This causes the curvate proximalportion 122 a of the head 122 to be increasingly compressed toward thebore 150 b until the head 122 is immovable in the seat 150 a.Ultimately, the compression surface 122 b seats in the recess 185 c andthereby is biased against retreat from the recess 185. This preventsaccidental reverse rotational slippage of the locking element 185 fromoccurring and moving the locking element to the unlocked position. Thelocking element 185 can still be moved back to the unlocked position ifthe surgeon desires to correct an error or to readjust the components,if the surgeon uses the wrenching tool 142 and applies enough force toovercome the force that seats the compression surface 122 b in therecess 185 c.

In addition, as the locking element 185 is moved to the locked position,the rod-receiving channel 190, presented by the locking element 185 whenthe locking element 185 is in the unlocked position, gradually closes.Ultimately, the channel 190 is completely closed. This prevents the rod195 from laterally exiting the locking element 185. Further, the walls190 a and 190 b of the channel 190 are gradually compressed toward oneanother, until they ultimately secure the rod 195 between them so thatthe rod 195 is fixed relative to the coupling element 150. This preventsthe rod 195 from axially exiting the locking element 185.

In addition, as the locking element 185 is moved to the locked position,the locking element 185 itself is gradually compressed within thecoupling element 150 until it ultimately is secured within the couplingelement 150. More specifically, as the rod 195 seeks to radially forcethe walls 190 a and 190 b apart, the outer surface of the lockingelement 185 seeks to radially push against the inner surface 150 c ofthe coupling element 150. However, the structural integrity of thecoupling element 150 resists the radial force of the locking element185, and the locking element 185 is secured in the coupling element 150thereby. This prevents the locking element 185 from axially exiting thecoupling element 150.

In this manner, once the locking element 185 is moved to the lockedposition, the screw 120, the coupling element 150, the locking element185, and the rod 195 are all fixed relative to one another and to thebone. When all of the locking elements 185 are so positioned, theimplant is installed. After the surgeon moves all of the lockingelements in the orthopedic rod implantation apparatus to the lockedposition, he closes the wounds of the patient and the surgery iscomplete.

While there has been described and illustrated embodiments of a screwand coupling element assembly, for use with an orthopedic rodimplantation apparatus, it will be apparent to those skilled in the artthat variations and modifications are possible without deviating fromthe broad spirit and principle of the invention. The invention shall,therefore, be limited solely by the scope of the claims appended hereto.

What is claimed is:
 1. A screw and coupling element assembly for usewith an orthopedic rod implantation apparatus, comprising: a screw thathas a head and a shaft that extends from the head; a coupling elementthat has a seat within which the head can be seated such that the shaftprotrudes from the coupling element; and a locking element that can bemated with the coupling element and that thereafter can be selectivelymoved through a plurality of positions including an unlocked positionand a locked position; wherein when the locking element is in theunlocked position, the locking element presents a rod-receiving channel,the rod-receiving channel is defined by substantially parallel walls,and the head is movable in the seat such that the shaft can be directedin a plurality of angles relative to the coupling element; and whereinwhen the locking element is in the locked position, a rod disposedwithin the rod-receiving channel is fixed relative to the couplingelement, the head is immovable in the seat such that the shaft is fixedat an angle relative to the coupling element, and the walls arecompressed toward one another such that the rod is compressed within thechannel and thereby fixed relative to the coupling element; and whereinthe head has a distal portion defined by a compression surface, thelocking element has a permissive surface that is presented to thecompression surface when the locking element is in the unlockedposition, and when presented with the permissive surface, thecompression surface is unhindered such that the head is movable in theseat; and wherein the locking element has a confrontational surface thatis presented to the compression surface when the locking element is inthe locked position, and the confrontational surface is defined by arecess that has a recessed surface corresponding to the compressionsurface; and wherein when the locking element is in the locked position,the locking element is compressed within the coupling element, aproximal portion of the head is compressed toward a bore in the couplingelement and the head is immovable in the seat, and the compressionsurface seats in the recess and thereby is biased against retreat fromthe recess.
 2. The assembly of claim 1, wherein the head has anengagement surface that can be engaged by a screwdriving tool, and atleast one of the elements has a bore that permits use of the tool whenthe head is seated in the seat.
 3. The assembly of claim 2, wherein oneof the head and the tool has a polygonal recess, and the other of thehead and the tool has an external structure that fits within thepolygonal recess.
 4. The assembly of claim 1, wherein the shaft extendsfrom the proximal portion of the head, the proximal portion is curvate,the seat is defined by the bore in the coupling element and a socketdefined by a curvate volume adjacent the bore, the curvate volumecorresponds to the curvate proximal portion such that the curvateproximal portion can be nested in the socket, and when the curvateproximal portion is nested in the socket, the shaft protrudes from thebore, the curvate proximal portion cannot pass fully through the bore,when the locking element is in the unlocked position the curvateproximal portion can rotate and angulate in the socket such that theshaft can be directed through a range of angles relative to the couplingelement, and when the locking element is in the locked position thecurvate proximal portion is immovable in the socket such that the shaftis fixed at an angle relative to the coupling element.
 5. The assemblyof claim 1, wherein the compression surface is a curvate surface, theconfrontational surface extends from an edge of the permissive surfaceand terminates in the recess, and the confrontational surface isgradually presented to the compression surface as the locking element ismoved from the unlocked position to the locked position.
 6. Anorthopedic rod implantation apparatus having screws and couplingelements, comprising: at least one elongate rod; and a plurality ofscrew and coupling element assemblies; wherein at least one of theassemblies comprises a screw that has a head and a shaft that extendsfrom the head, a coupling element that has a seat within which the headcan be seated such that the shaft protrudes from the coupling element,and a locking element that can be mated with the coupling element andthat thereafter can be selectively moved through a plurality ofpositions including an unlocked position and a locked position; andwherein when the locking element is in the unlocked position, thelocking element presents a rod-receiving channel, the rod-receivingchannel is defined by substantially parallel walls, and the head ismovable in the seat such that the shaft can be directed in a pluralityof angles relative to the coupling element; and wherein when the lockingelement is in the locked position, the rod, if disposed within therod-receiving channel, is fixed relative to the coupling element, andthe head is immovable in the seat such that the shaft is fixed at anangle relative to the coupling element; and wherein the head has adistal portion defined by a compression surface, the locking element hasa permissive surface that is presented to the compression surface whenthe locking element is in the unlocked position, and when presented withthe permissive surface, the compression surface is unhindered such thatthe head is movable in the seat; and wherein the locking element has aconfrontational surface that is presented to the compression surfacewhen the locking element is in the locked position, and theconfrontational surface is defined by a recess that has a recessedsurface corresponding to the compression surface; and wherein when thelocking element is in the locked position, the locking element iscompressed within the coupling element, the compression surface iscompressed by the confrontational surface such that a curvate proximalportion of the head is compressed toward a bore in the coupling elementand the head is immovable in the seat, the walls are compressed towardone another such that the rod is compressed within the channel andthereby fixed relative to the coupling element, and the compressionsurface seats in the recess and thereby is biased against retreat fromthe recess.
 7. The apparatus of claim 6, wherein the head has anengagement surface that can be engaged by a screwdriving tool, and atleast one of the coupling element and the locking element has a borethat permits use of the tool when the head is seated in the seat.
 8. Theapparatus of claim 7, wherein one of the head and the tool has apolygonal recess, and the other of the head and tool has an externalstructure that fits within the polygonal recess.
 9. The apparatus ofclaim 6, wherein the shaft extends from the curvate proximal portion ofthe head, the proximal portion is curvate, the seat is defined by thebore in the coupling element and a socket defined by a curvate volumeadjacent the bore, the curvate volume corresponds to the curvateproximal portion such that the curvate proximal portion can be nested inthe socket, and when the curvate proximal portion is nested in thesocket, the shaft protrudes from the bore, the curvate proximal portioncannot pass fully through the bore, when the locking element is in theunlocked position the curvate proximal portion can rotate and angulatein the socket such that the shaft can be directed through a range ofangles relative to the coupling element, and when the locking element isin the locked position the curvate proximal portion is immovable in thesocket such that the shaft is fixed at an angle relative to the couplingelement.
 10. The apparatus of claim 6, wherein the compression surfaceis a curvate surface, the confrontational surface extends from an edgeof the permissive surface and terminates in the recess, and theconfrontational surface is gradually presented to the compressionsurface as the locking element is moved from the unlocked position tothe locked position.
 11. A locking assembly, comprising: a securingelement that has a head and a shaft that extends from the head; acoupling element that has a seat within which the head can be seatedsuch that the shaft protrudes from the coupling element, the seat isdefined by a bore in the coupling element and a socket adjacent the borewherein the head can be nested in the socket such that head cannot passfully through the bore but the shaft protrudes from the bore; and alocking element that can be mated with the coupling element and thatthereafter can be selectively moved through a plurality of positionsincluding an unlocked position and a locked position, the lockingelement has an increasingly confrontational surface terminating in arecess that has a recessed surface; wherein when the locking element isin the unlocked position, the locking element presents a channel forreceiving a rod and the head has a compression surface corresponding tothe recessed surface; and the channel is defined by walls of the lockingelement, and the head is movable in the seat such that the shaft can bedirected in a plurality of angles relative to the coupling element;wherein when the locking element is in the locked position, the rod, ifdisposed within the channel, is fixed relative to the coupling element,the head is immovable in the seat such that shaft is fixed at an anglerelative to the coupling element, the locking element is compressionlocked within the coupling element, the head is compression lockedwithin the seat, and the rod, if disposed within the channel, iscompression locked within the channel; wherein: when the locking elementis moved from the unlocked position to the locked position: the lockingelement is compressed within the coupling element; the walls arecompressed toward one another such that the rod, if disposed within thechannel, is compressed within the channel and thereby fixed relative tothe coupling element; the compression surface is compressed by theconfrontational surface such that the head is compressed toward the boreand rendered immovable in the socket; and the compression surface seatsin the recess and thereby is biased against retreat from the recess. 12.The assembly of claim 11, wherein the locking element is moved throughthe plurality of positions by rotating the locking element within thecoupling element.
 13. The assembly of claim 11, wherein the lockingelement is provided with at least one engagement surface that can beengaged by a tool to move the locking element through the plurality ofpositions.
 14. The assembly of claim 13, wherein the tool has acorresponding surface that engages the engagement surface and the toolaccommodates the rod as the tool is used to move the locking elementthrough the plurality of positions.